Compact Oxygen Heat Exchanger for the Exploration Portable Life Support System

The ventilation loop in NASA’s Exploration Portable Life Support System (xPLSS) includes a compact heat exchanger that cools the ventilation gas before it enters the suit helmet. This heat exchanger must provide efficient gas cooling with low pressure losses in a very compact package. It must operate across a wide range of suit pressures and be built from materials that are compatible with oxygen and the thermal control loop. Finally, the heat exchanger must serve as a pressure drop element that can be used to measure the ventilation flow rate with high accuracy.

We have developed an innovative heat exchanger that meets these requirements. The miniature shell-and-tube heat exchanger uses a core built from an array of Inconel microtubes. The microtubes provide a very high surface area and high heat transfer coefficients for efficient gas cooling with minimal pressure losses in the ventilation and thermal control loops.

We have designed and built several generations of the heat exchanger and measured their heat transfer and pressure drop performance in an extensive series of tests that simulate operation in the xPLSS ventilation loop. We have found that the compact heat exchanger meets all xPLSS requirements for heat transfer and pressure loss. The heat exchanger is designed for close integration with a high-accuracy flow meter, and produces a highly linear flow vs. pressure drop characteristic that is suitable for high-accuracy flow measurement.

Two units have been delivered to NASA in 2019 and three additional development, verification, and test (DVT) units are scheduled for delivery in 2020. This paper will describe the design, manufacturing, and performance of the DVT heat exchangers.